<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>高度塌陷</title>
    <style>
        .box1{
            border: 1px solid red;
        }
        .box1::after{
            content: "";
            clear: both;
            display: block;
        }
        .box2{
          width: 100px;
          height: 200px;
          background-color: aqua; 
          float: left; 
        }
        .box3{
            width: 100px;
            height: 100px;
            background-color: antiquewhite;
            outline: 1px solid black ;
            /* float: left; */
            /* display: inline-block; */
            /* 开启隐藏的BFC属性 */
            /* overflow: hidden; */
            /* clear: left; */
        }
    </style>
</head>
<body>
    <div class="box1">
        <div class="box2">

        </div>
    </div>
    <div class="box3">

    </div>
</body>
</html>